1. Field of the Invention
The invention relates to apparatus and methods for signaling communications in a packet data network, such as a 3rd Generation Partnership Project (3GPP) cellular communication system.
2. Background of the Invention
Currently, 3rd generation cellular communication systems are being rolled out to further enhance the communication services provided to mobile phone users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple Access (CDMA) and Frequency Division Duplex (FDD) or Time Division Duplex (TDD) technology. Further description of CDMA, and specifically of the Wideband CDMA (WCDMA) mode of UMTS, can be found in ‘WCDMA for UMTS’, Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.
In 3GPP systems, such as the General Packet Radio System (GPRS), Evolved Packet System (EPS), the downlink communication endpoint, namely the mobile or handheld wireless communication unit, referred to as user equipment (UE) in 3G parlance, may have multiple simultaneous connections to a number of network elements. Such network elements typically comprise gateways (GWs), such as General GPRS Support nodes (GGSNs), packet data network (PDN) GWs, etc., in order to obtain access to different Packet Data Networks (PDNs) that facilitate the UE accessing a number of different services (for example facilitating access to corporate services as well as simultaneous access to the Internet).
In such systems, the amount of data being transferred between elements may be controlled by setting an aggregate maximum bit rate (AMBR), which is defined as an upper limit for non-guaranteed bit rate (GBR) communication bearers that are associated with a particular PDN connection that a UE has established.
FIG. 1 illustrates a known 3GPP system 100 that uses AMBR. The 3GPP system 100 comprises a UE 105 communicating with two independent PDNs, PDN-1 135 and PDN-2 145 via first and second access point nodes 130, 140 respectively, which are shown as GWs.
The respective data streams to the PDNs are routed by a Mobility Management Entity (MME) 120, which is coupled to Authentication, Authorization and Accounting (AAA) Server 125. The totality of these network elements is often referred to as a core network 115. A Node-B 110 routes the wireless transmission from the UE 105 to the MME 120 in the core network 115. In order to utilize an AMBR to limit a data amount sent to the respective PDNs, the AMBR needs to be enforced for each of the Non-Guaranteed Bit Rate (GBR) bearers connecting the UE with a particular GW providing access to a specific PDN.
In 3GPP (see, for example, 3GPP TS 23.401, ‘GPRS enhancements for E-UTRAN access’; Release 8) the AMBR is enforced in the NodeB 110 in 3GPP for the UpLink (UL) traffic and in the GW (for example PDN-1 and PDN-2 GWs in 3GPP) for the respective DownLink (DL) traffic. This is a natural choice given that the NodeB and GWs are the traffic ingress points for the UL and DL traffic respectively. Furthermore, as radio resources are the most cost sensitive for a wireless Operator, it is not reasonable to ‘pass through’ UL traffic over an air-interface when the UL traffic will be later discarded.
Thus, the Node B 110 has to be informed of the PDN connections that the UE 105 has established at any time and be in a position to associate the radio bearer that it assigns scheduling priorities with the UE-PDN connection that it belongs to. In other words the Node B 110 has to take into account the AMBR value and its relationship with each UE-PDN connection to the UL scheduling decisions it makes (for example by assignment of a prioritized bit rate PBR). The Node-B 110 also controls the radio bearer establishment and management. According to the information received from the relevant Core Network (CN) 115 element, for example MME 120 in the 3GPP Evolved Packet System (EPS), the Node B 110 establishes the radio bearers for all the corresponding gateways (GW).
The characteristics of AMBR are somewhat different to other dynamic bearer parameters that are used in wireless and other communication systems to support a particular end-to-end QoS, in the sense that:
(i) An AMBR value is applied to a ‘bundle’ of Non-GBR bearers, for a specific UE-PDN connection, and not each one individually. Therefore, AMBR values require a special treatment by the network element that is responsible to enforce and police the AMBR, particularly when this element is responsible to schedule resources that are dynamically changing (such as the Node-B); and
(ii) The AMBR value is static subscriber information, stored in the subscriber database registry. Therefore, the AMBR value has to be communicated during the initial attach procedure, instead of being dynamically provided by the Policy Server as part of the bearer setup, in contrast to how the other dynamically changing QoS parameters are normally provided.
FIG. 2 illustrates a known radio bearer establishment mechanism between the UE 105 and the Node-B 110, and the AMBR policing performed in the UL and DL respectively. It is noteworthy that a one-to-one relationship between the radio bearer 205 that connects the UE 105 to the Node-B 110 and access bearer 210 that terminates the traffic to the PDN GW 130 is maintained at the radio bearer 205 establishment. At a given time, there may be more than one radio bearer 205 and access bearer 210 established to the UE 105 for the purposes of providing different Quality of Service (QoS) treatment to different user applications or classes of users. In the DL, the logical elements of the scheduler in the Node-B 110 schedules the DL traffic based on a particular Quality of Service (QoS) of the radio bearers 205 that has been indicated to it by some QoS identifier during the bearer establishment as well as traffic volume used in the respective radio bearers 205. The AMBR policing for the DL traffic is carried out at the respective PDN GW 130, 135, 140, 145, given this is where the 3GPP Policy and Charging Enforcement Function (PCEF) is typically located since the PDN GWs 130, 140 are the first ingress points of downlink (DL) traffic.
If an AMBR level is exceeded in the DL, for a particular PDN connection, the exceeding traffic for all the access (non-GBR) bearers 210 from this PDN GW may be rate limited by the 3GPP PCEF in the PDN GW, in order to conform to the specified AMBR that has been communicated to the PDN GW at the initial bearer establishment.
Thus, UL resource is assigned by the appropriate logical element of the scheduler in the Node-B 110 according to the traffic volume reported by the UE, and allocated on a per UE basis. The scheduling of radio bearers 205 into the allocated grant is performed by the UE 105 using the logical function of the UL packet scheduler based on priorities that are communicated to it at the radio bearer establishment by the Node-B 110. In order to control the radio bearer scheduling by the UE 105, an UL rate control function that manages the sharing of UL resources between radio bearers has been specified in 3GPP. The scheduler in the Node-B 110 configures each radio bearer 205 with scheduling parameters, such as an absolute priority value and a Prioritized Bit Rate (PBR) value, based on the Quality of Service (QoS) parameters that are communicated by the core network (CN), such as the QoS label and the GBR value for the GBR bearers. In addition, a maximum bit rate (MBR) may be optionally configured per radio bearer 205. The assigned priority value and the PBR are signaled to the UE 105 together with the radio bearer configuration information. The priority value is decided by the Node-B 110 based on the QoS information received from the Core Network (CN) 115. In this manner, the PBR sets an UL rate control limit at the UE that applies per radio bearer and ensures that the UE 105 serves its radio bearers 205 in decreasing priority order up to their PBR value.
If any resources remain available, all the radio bearers 205 are served in a strictly decreasing priority order, up to their MBR (if configured). In a case where no MBR is configured, the radio bearer 205 is served until either the data for that radio bearer 205 or the UL grant is exhausted, whichever occurs first. In general terms these parameters are the scheduling priority parameters that apply in the case of a 3GPP long-term evolution (LTE) wireless communication system.
However, the inventors have recognized and appreciated that the assignment of these scheduling parameters (for example PBR, priority and (optionally) MBR in a case of a 3GPP LTE wireless communication system) are not associated with the AMBR that applies to the entire UE-PDN connection that this radio bearer serves. This means, in effect, that if two bearers have the same QoS characteristics (for example, QoS label) and even though they belong to two different PDN connections (for example one with high AMBR values and one with low AMBR values), both radio bearers will receive the same scheduling treatment given that the AMBR is not communicated to the Node-B. Thus, this scenario is inefficient and wasteful of valuable resource. For example, if a bearer serves hyper text transfer protocol (HTTP) traffic from a virtual private network (VPN) with high AMBR and HTTP traffic from the Internet with a low AMBR, the same scheduling treatment at the Node-B 110 and the UE 105 will apply to both.
Consequently, current techniques are suboptimal. Hence, an improved mechanism to address the problem of handling AMBR over a cellular network would be advantageous.